Small Renal Mass with Extensive Inferior Vena Cava Tumor Thrombus: A Rare Clinical Paradox

Abstract

Renal cell carcinoma (RCC) commonly demonstrates venous invasion; however, the occurrence of extensive inferior vena cava (IVC) tumor thrombus arising from a small renal mass is distinctly uncommon. We report a case of a 60-year-old female presenting with low backache and weight loss. Contrast-enhanced positron emission tomography-computed tomography revealed a 3.6-cm exophytic left renal mass with fluorodeoxyglucose-avid tumor thrombus extending from the left renal vein into the retrohepatic IVC below the hepatic veins. The patient underwent open left radical nephrectomy with IVC thrombectomy. Histopathology revealed conventional clear cell RCC measuring 4 cm × 3.5 cm × 3 cm with World Health Organization/International Society of Urological Pathology grade 4 features, tumor necrosis, sarcomatoid and rhabdoid differentiation, renal sinus fat invasion, and lymphovascular emboli. The final pathological staging was pT3bN0. This case highlights that tumor size alone may not reflect biological aggressiveness in RCC. Thorough vascular evaluation is essential even in apparently localized small renal tumors.